Nitriding method of gate oxide film

ABSTRACT

A substrate processing method comprises the step of forming an oxide film on a silicon substrate surface, and introducing nitrogen atoms into the oxide film by exposing the oxide film to nitrogen radicals excited in plasma formed by a microwave introduced via a planar antenna.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention is a continuous-in-part application ofPCT/JP2003/006080 filed on May 15, 2003 based on Japanese PatentApplication 2002-141654 filed on May 16, 2002, the entire contents ofthese are incorporated herein as reference.

BACKGROUND OF THE INVENTION

The present invention generally relates to substrate processing methodand more particularly to a nitriding method of an oxide film formed on asilicon substrate surface.

With progress in the art of device miniaturization, fabrication ofultrafine semiconductor devices having a gate length of less than 0.1 μmis now becoming possible.

In order to achieve improvement of operational speed of thesemiconductor device with such ultrafine semiconductor devices by way ofdecrease of the gate length, there is a need to decrease the thicknessof the gate insulation film according to scaling law. In the case ofusing a conventional thermal oxide film for the gate insulation film,for example, it is necessary to reduce the thickness of the gateinsulation film to be equal to or smaller than the conventionalthickness of 1.7 nm. However, such a decrease of thickness of the oxidefilm invites increase of the gate leakage current through the oxide filmas a result of tunneling effect.

Thus, there have been studies to use a high-K dielectric film such asTa₂O₅ or ZrO₂ for the gate insulation film in place of the conventionalsilicon oxide film. However, these high-K dielectric films have a naturevery much different from that of the silicon oxide film usedconventionally in the semiconductor technology, and there remainnumerous problems to be solved before such high-K dielectric film isused for the gate insulation film.

Contrary to this, a silicon nitride film has a material usedconventionally in the semiconductor processes, and is thought as being apromising material for the gate insulation film of the next-generationhigh-speed semiconductor devices in view of its specific dielectricconstant, which is twice as large as that of a silicon oxide film.

Conventionally, a silicon nitride film has been formed on an interlayerinsulation film by a plasma CVD process. However, such a CVD nitridefilm generally has the feature of large leakage current, and the usethereof for a gate insulation film has been inappropriate. In fact, noattempts have been made conventionally to use a nitride film for a gateinsulation film.

Meanwhile, there have been proposed recently the technology of nitridinga surface of a silicon oxide film and convert the same to an oxynitridefilm by generating N radicals or NH radicals by introducing a gascontaining nitrogen such as a nitrogen gas, nitrogen and hydrogen gasesor an NH₃ gas into microwave-excited rare gas plasma of Ar, Kr, or thelike. The oxynitride film thus formed has the feature of smalloxide-film equivalent thickness and also the feature of leakage currentcharacteristics comparable to or even surpassing that of a thermal oxidefilm, and thus, the oxynitride film thus formed is thought as being apromising material for the gate insulation film of the next-generationhigh-speed semiconductor devices. Further, the oxynitride film thusformed is chemically stable, and it is possible to suppress, in the casea high-K dielectric film is formed on the oxynitride film, the diffusionof metal elements in the high-K dielectric film through the oxynitridefilm and associated reaction of the high-K dielectric film with thesilicon substrate caused by way of such diffusion. Further, there isproposed a technology of directly nitriding a silicon substrate surfaceby such microwave plasma.

Conventionally, it has been known to introduce nitrogen into an oxidefilm by a thermal annealing process conducted in nitrogen ambient or byan implantation of nitrogen ions. On the other hand, it is known thatthe nitrogen atoms introduced according to such a process predominantlyconcentrate in the vicinity of the interface between the siliconsubstrate and the oxide film. As a result, in the case such aconventional oxynitride film is used for the gate insulation film of aMOS transistor, there are caused problems such as variation of thethreshold voltage or degradation of mobility caused by formation of theinterface states.

Because of similar reasons, there can be caused deterioration ofsemiconductor device characteristics also in the case of an oxynitridefilm processed by N radicals or NH radicals is used, instead of thedesired improvement of semiconductor device characteristics, unless thedistribution of the nitrogen atoms in the film is controlledappropriately.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to providea novel and useful substrate processing method wherein the foregoingproblems are eliminated.

Another object of the present invention is to provide a nitridationmethod of an oxide film capable of optimizing distribution of nitrogenatoms in the film.

Another object of the present invention is to provide a substrateprocessing method, characterized by the steps of:

forming an oxide film on a silicon substrate surface;

introducing nitrogen atoms into said oxide film by exposing said oxidefilm to nitrogen radicals or nitrogen ions excited in microwave plasma.

According to the present invention, it becomes possible to obtain anoxynitride film having optimum characteristics including the leakagecurrent characteristics by choosing processing pressure according to aninitial film thickness of the oxide film at the time of nitriding anoxide film by microwave-excited nitrogen radicals.

Other objects and further features of the present invention will becomeapparent from the following detailed description when read inconjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are diagrams showing the construction of a microwaveplasma processing apparatus used with the present invention;

FIGS. 2A-2C are diagrams showing the oxidation processing of a siliconsubstrate and nitridation processing of an oxide film conducted by thesubstrate processing apparatus of FIGS. 1A and 1B according to a firstembodiment of the present invention;

FIG. 3 is a diagram showing the distribution of the nitrogen atoms inthe oxynitride film obtained with an embodiment of the presentinvention;

FIG. 4 is a diagram showing the time-dependent change of the nitrogenatom distribution in the oxynitride film of FIG. 3;

FIG. 5 is a diagram showing the relationship between the leakage currentand the oxide-film equivalent thickness of the oxide film associatedwith the nitridation process of the present embodiment;

FIG. 6 is another diagram showing the relationship between the leakagecurrent and the oxide-film equivalent thickness of the oxide filmassociated with the nitridation process of the present embodiment;

FIGS. 7A-7C are diagrams showing the oxidation processing of a siliconsubstrate and nitridation processing of an oxide film according to asecond embodiment of the present invention;

FIGS. 8A and 8B are diagrams respectively showing the overallconstruction of the substrate processing system according to a thirdembodiment of the present invention including the substrate processingapparatus of FIGS. 1A and 1B and used with the present invention forsubstrate processing and the construction of a computer used forcontrolling the substrate processing system of FIG. 8A;

FIG. 9 is a flowchart of the computer-controlled processing according tothe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the investigation constituting the foundation of the presentinvention, the inventor of the present invention has discovered, in theexperiments of nitriding an oxide film by nitrogen radicals excited byAr gas plasma, that the distribution of the nitrogen atoms in the filmchanges significantly depending on the nitridation processing condition,especially the processing pressure and processing time.

Thus the object of the present invention is to provide, based on theforegoing knowledge, a nitridation method of an oxide film capable ofoptimizing the distribution of the nitrogen atoms in the film.

First Embodiment

FIG. 1A shows the schematic construction of a plasma processingapparatus 10 used with the present invention.

Referring to FIG. 1A, the plasma substrate processing apparatus 10includes a processing vessel 11 in which a processing space 11A isformed such that a stage 12 holding a substrate W to be processedthereon is formed in the processing space 11A, wherein the processingvessel 11 is evacuated by an evacuation system 11E at an evacuation port11C via a space 11B surrounding the stage 12 and an adaptive pressurecontroller 11D.

The stage 12 is provided with a heater 12A, wherein the heater 12A isdriven by a power source 12C via a line 12B.

Further, the processing vessel 11 is provided with a substrate in/outopening 11 g and a gate valve 11G cooperating therewith for loading andunloading of the substrate W to be processed to and from the processingvessel 11.

On the processing vessel 11, there is formed an opening incorrespondence to the substrate W to be processed on the stage 12, andthe opening is closed by a top plate 13 of quartz or a low-loss ceramicsuch as alumina or AlN. Further, underneath the top plate 13, there areformed a gas ring 14 formed with a gas inlet path and a large number ofnozzle openings communicating therewith such that the gas ring 14 facesthe substrate W to be processed.

It should be noted that the cover plate 13 forms a microwave window, anda flat microwave antenna 15 of a radial line slot antenna or a hornantenna is provided on the top part of the top plate 13.

In the illustrated example, a radial line slot antenna is used for theflat microwave antenna 15, wherein it should be noted that the radialline slot antenna includes a flat antenna main part 15A and a radiationplate 15C, wherein the radiation plate 15C is provided at the openingpart of the flat antenna main part 15A via a retardation plate 15B ofquartz or alumina.

The radiation plate 15C is provided with a large number of slots 15 aand 15 b as will be explained with reference to FIG. 1B, wherein theradial line slot antenna 15 is connected to a coaxial waveguide 16having an outer conductor 16A connected to the antenna main part 15A ofthe radial line slot antenna 15 and a central conductor 16B connected tothe radiation plate 15C through the retardation plate 15B. The coaxialwaveguide 16 is connected to a rectangular waveguide 110B via a modeconversion part 110A, wherein the rectangular waveguide 110B isconnected to a microwave source 112 via an impedance matcher 111.Thereby, the microwave source 112 supplies a microwave to the radialline slot antenna 15 via the rectangular waveguide 110B and the coaxialwaveguide 16.

FIG. 1B shows the construction of the radial line slot antenna.

Referring to FIG. 1B showing the radiation plate 15C in a plan view, itcan be seen that the slots 15 a and 15 b are formed in a concentricrelationship in such a manner that a slot 15 a and an adjacent slot 15 bform an angle of 90 degrees.

Thereby, the microwave supplied from the coaxial waveguide 16 spreads inthe radial direction in the radial line slot antenna 15 with wavelengthcompression caused by the retardation plate 15B. Thereby, the microwaveis emitted from the slits 15 a and 15 b generally in the directionperpendicular to the plane of the radiation plate 15C in the form of acircular polarized microwave.

Further, as shown in FIG. 1A, a rare gas source 101A such as an Ar gassource and a nitrogen gas source 101B are connected to the gas ring 14via respective mass flow controllers 103A and 103N and via respectivecorresponding valves 104A, 104N, 105A, 105N and a common valve 106. Asnoted before, the gas ring 14 is provided with a large number of gasinlet ports around the stage 12 uniformly, and the rare gas and thenitrogen gas supplied to the gas ring 14 are introduced into theprocessing space 14A inside the processing vessel 11 uniformly. Inaddition, an oxygen gas source 101O is connected to the gas ring 14 viaa mass flow controller 103O and valves 104O and 105O in the illustratedexample for supplying oxygen to the processing vessel 11.

In operation, the processing space inside the processing vessel 11 isset to a predetermined pressure by evacuating through the evacuationport 11C, and an oxidizing gas or a nitriding gas is introduced from thegas ring 14 together with an inert gas such as Ar, Kr, Xe, Ne, Ne (raregas) and the like.

Further, a microwave having the frequency of several GHz such as 2.45GHz is introduced from the microwave source 112 via the antenna 15, andthere is excited high-density microwave plasma in the processing vessel11 at the surface of the substrate W to be processed with a plasmadensity of 10¹¹-10¹³/cm³. By exciting the plasma by the microwaveintroduced via the antenna, the plasma has low electron temperature of0.7-2 eV or less, preferable 1.5 eV or less, with the substrateprocessing apparatus of FIG. 1A, and damaging of the substrate W or theinner wall of the processing vessel is avoided. Further, the radicalsthus formed are caused to flow in the radial direction along the surfaceof the substrate W to be processed and are evacuated promptly. Thereby,recombination of the radicals is suppressed, and an extremely uniformand efficient substrate processing is realized at the low temperature of550° C. or less.

FIGS. 2A-2C show the substrate processing process according to anembodiment of the present invention that uses the substrate processingapparatus 10 of FIGS. 1A and 1B.

Referring to FIG. 2A, a silicon substrate 21 is introduced into theprocessing vessel 11 of the substrate processing apparatus 10 as asubstrate W to be processed, and a mixed gas of Kr and oxygen isintroduced from the gas ring 14. Further, atomic state oxygen O* (oxygenradial) is formed by exciting the same with microwave-plasma. As aresult of processing of the surface of the silicon substrate 21 withsuch atomic state oxygen O*, there is formed a silicon oxide film 22 onthe surface of the silicon substrate 21 with the thickness of 1.6 nm asshown in FIG. 2B. The silicon oxide film 22 thus formed has a leakagecurrent characteristic comparable with that of a thermal oxide filmformed at a high temperature of 700° C. or more, in spite of the factthat it is formed at a very low temperature of about 400° C.Alternatively, the silicon oxide film 22 may be a thermal oxide film.

Next, in the step of FIG. 2C, a mixed gas of Ar and nitrogen isintroduced into the processing vessel 11 in the substrate processingapparatus 10 of FIGS. 1A and 1B, and excitation of plasma is made bysupplying a microwave power while setting the substrate temperature toabout 400° C.

In the step of FIG. 2C, it should be noted that the internal pressure ofthe processing vessel 11 is set to 5-7 Pa and the Ar gas is suppliedwith the flow rate of 1000 SCCM, for example. Further, the nitrogen gasis supplied with the flow rate of 40 SCCM, for example. As a result, thesurface of the silicon oxide film 22 is nitrided and is converted to asilicon oxynitride film 22A.

FIG. 3 shows the SIMS profile showing the distribution of the oxygenatoms and nitrogen atoms (continuous line A) in the oxynitride film 22Athus processed with the nitridation processing.

Referring to FIG. 3, the interface between the oxynitride film 22A andthe silicon substrate 21 is located at the depth of about 1.6 nm, and itcan be seen that there appears a maximum concentration of the nitrogenatoms at the central part of the oxynitride film 22A in the thicknessdirection. Further, the result of FIG. 3 indicates that the nitrogenatoms distribute generally in the entirety of the oxynitride film 22Aexcept for the film surface and the region right underneath the filmsurface, while this also means that there exits substantial amount ofnitrogen atoms also in the vicinity of the interface between theoxynitride film 22A and the silicon substrate 21.

FIG. 3 also shows the distribution of the nitrogen atoms in theoxynitride film 22A for the case the processing of FIG. 2C is conductedunder the same condition except that the processing pressure is changedto 60-130 Pa by a broken line B.

Referring to FIG. 3 again, it will be noted that the number of thenitrogen atoms incorporated into the oxynitride film 22A is decreased inthe case the nitridation processing of FIG. 2C is conducted under such ahigh processing pressure, as compared with the case the processingpressure is low, and associated with this, the nitrogen concentration inthe film is reduced also. Particularly, in the case the nitridationprocessing is conducted under such a high processing pressure, it willbe noted that the nitrogen concentration in the vicinity of theinterface between the oxynitride film 22A and the silicon substrate 21is below the detection limit and that there exist little nitrogen insuch a part.

Thus, by conducting the nitridation processing of the oxide film of FIG.2C at high processing pressure, it becomes possible to restrict thedistribution of the nitrogen atoms in the oxynitride film 22A at theshallow part thereof. By using such an oxynitride film 22A for the gateinsulation film of a MOS transistor, it becomes possible to eliminatethe problem of degradation of the carrier mobility or variation of thethreshold voltage caused by the existence of the nitrogen atoms in thevicinity of the interface between the oxynitride film 22A and thesilicon substrate.

FIG. 4 is a diagram showing the time-dependent change of thedistribution of the nitrogen atoms in the film for the case thenitridation processing of FIG. 2C is conducted at a high pressure of60-130 Pa (broken line) and the case in which the nitridation processingis conducted at a low processing pressure (continuous line).

Referring to FIG. 4, it will be noted that the depth of penetration ofthe nitrogen atoms in the oxynitride film 22A is limited in the case theprocessing pressure is high, and thus, it is concluded that thenitridation processing conducted at a high processing pressure exceeding60 Pa is suited for introducing nitrogen only to a part of an extremelythin oxide film such as the one having the thickness of 1 nm or less. Onthe other hand, in the case the processing pressure is low, the nitrogenatoms distribute over the entirety of the oxide film, and thus, thenitridation processing under low processing pressure of 60 Pa or less issuitable for uniformly nitriding an oxynitride film of relatively largethickness such as the one having the thickness of 1 nm or more.

It is believed that the results of FIGS. 3 and 4 reflect the situationthat, in the case the processing pressure is increased in thenitridation processing of FIG. 2C, there is caused a decrease ofelectron temperature and the nitrogen ions formed in the plasma are lesssusceptible for acceleration in the direction toward the substrate.Thereby, the nitrogen ions are deactivated before they reach thesubstrate and cause nitridation therein. In the case the processingpressure is set low, on the other hand, there occurs increase ofelectron temperature, and the nitrogen ions are accelerated toward thesubstrate. Thereby, the nitrogen ions reach the substrate in the activestate and facilitate the nitridation therein.

FIG. 5 shows the leakage characteristics of an N-type MOS capacitor inwhich the oxynitride film formed according to the method of the presentinvention is used for the gate insulation film. In FIG. 5, it should benoted that the oxynitride film is formed by two methods, the first beingthe one conducting the nitridation processing of FIG. 2C for the oxidefilm having the thickness of 1.6 nm under a high processing pressure of60-130 Pa for various processing durations and the second being the oneconducting the nitridation processing of FIG. 2C for the oxide filmhaving the thickness of 1.6 nm under a low pressure of 5-7 Pa, whereinthe vertical axis represents the gate leakage current density Jg for thecase a gate voltage of −1.8V is applied, while the horizontal axisrepresents the oxide-film equivalent thickness Tox.

In FIG. 5, the broken line shows the results for the case of using thehigh processing pressure, while the continuous line represents the caseof using the low processing pressure.

Referring to FIG. 5, it will be noted that there is caused a decrease inthe oxide-film equivalent thickness Tox when the nitridation processingof FIG. 2C is conducted under the foregoing low processing pressure toabout 1.4 nm as a result of penetration of the nitrogen atoms into theoxide film, and there is also achieved suppression of increase of theleakage current. On the other hand, when the nitridation processing iscontinues for a long time, there is caused a turn-around phenomenon, andthe leakage current starts to decrease, while this decrease of theleakage current is accompanied with increase of the oxide-filmequivalent thickness Tox. It is believed that this reflects thesituation that, with extensive invasion of the nitrogen atoms into theoxide film 12 at the time of formation of the oxynitride film 12A, theoxygen atoms in the film start to invade into the silicon substrate,resulting in the increase of the physical thickness of the oxynitridefilm 12A. It should be noted that such invasion of the oxygen atoms intothe silicon substrate causes deterioration in the interface between theoxynitride film 12A and the silicon substrate 12. Thus, at the time offorming the oxynitride film 12A by introducing nitrogen into the oxidefilm 12 in the step of FIG. 2C, it becomes possible to minimize theoxide-film equivalent thickness Tox of the oxynitride film 12A withoutdeteriorating the film quality, by realizing the state immediatelybefore the turn-around.

In the case the nitridation processing of FIG. 2C is conducted under thehigh processing pressure, on the other hand, the amount of the nitrogenatoms incorporated into the film is small, and thus, the decrease of theoxide-film equivalent thickness is small as represented in FIG. 5 by thebroken line. On the other hand, the increase of the leakage currentassociated with the decrease of the oxide film equivalent thickness issuppressed further. Thus, it should be noted that the gradient of thecurve shown in FIG. 5 is smaller than the gradient of the curverepresented by the continuous line.

Thus, in the case the allowable leakage current is 1 A/cm² for theapplied voltage of −1.8V as shown in FIG. 6, it will be noted that thisallowable leakage current is exceeded when the nitrogen atoms areintroduced with the nitridation processing at 5-7 Pa, provided that theoxide film has the initial thickness of 1.45 nm in the state of FIG. 2B,as represented by an arrow A.

In the example of FIG. 6, it will be noted that, in the case the oxidefilm 12 has the initial thickness of about 1.6 nm as shown by the arrowB, the leakage current density immediately before the turn around pointis generally equal to the allowable limit value, provided that theforegoing nitridation processing is conducted at the low pressure of 5-7Pa. From this, it is concluded that the leakage current exceeds theallowable limit in the case the nitridation processing is conductedunder the low pressure of 5-7 Pa for the oxide film 12 having theinitial thickness of 1.6 nm or less and that it is preferable to conductthe foregoing nitridation processing under the high pressure of 60-130Pa, not with the foregoing low pressure.

In the case the nitridation processing is conducted in the pressurerange of 60-130 Pa, the proportion of increase of the leakage currentassociated with the decrease of the equivalent thickness is small, andthus, the requirement of the leakage current value of 1 A/cm² issatisfied even in the case the initial thickness if less than 1.6 nm.

On the other hand, when the initial thickness of the oxide film exceeds1.6 nm, it is preferable to set the processing pressure of thenitridation processing of FIG. 2C to be less than 30 Pa, preferably 5-7Pa.

Thus, according to the present invention, it becomes possible toachieve, at the time of nitridation processing of an oxide film, theleakage current of the obtained oxynitride film to fall within a desiredallowable range, by choosing the processing pressure of the nitridationprocessing in response to the thickness of the initial film thickness ofthe oxide film.

Second Embodiment

FIGS. 7A-7C show the substrate processing process according to secondembodiment of the present invention that uses the substrate processingapparatus 10 of FIGS. 1A and 1B.

Referring to FIG. 7A, a silicon substrate 41 is processed with aso-called wet oxidation process by processing the silicon substrate 41in a furnace supplied with H₂O (moisture).

With such a wet oxidation processing, there is formed a silicon oxidefilm 42 on the surface of the silicon substrate 41 with the thickness ofabout 1 nm as shown in FIG. 7B.

Further, in the step of FIG. 7C, a mixed gas of Ar and nitrogen isintroduced into the processing vessel 11 in the substrate processingapparatus 10 of FIGS. 1A and 1B, and excitation of plasma is made bysupplying a microwave while setting the substrate temperature to about400° C.

In the step of FIG. 4C, the internal pressure of the processing vessel11 is set to 5-7 Pa, and the Ar gas is supplied with the flow rate of1000 SCCM, for example. Further, the nitrogen gas is supplied with theflow rate of 40 SCCMM, for example. As a result, the surface of theoxide film 42 is nitrided and is converted to a silicon oxynitride film42A, similarly to the process of FIG. 2C.

Third Embodiment

FIG. 8A shows the construction of an overall substrate processing system100 that includes the substrate processing apparatus 10 of FIGS. 1A and1B and used for the nitridation processing of the oxide film of thepresent invention, while FIG. 7B shows a computer used for controllingthe substrate processing apparatus 10 of FIGS. 1A and 1B in the systemof FIG. 8A.

Referring to FIG. BA, the system 100 includes the Ar gas source 101A,the nitrogen gas source 101B and the oxygen gas source 101O, wherein theAr gas source 101A supplies an Ar gas to the gas ring 14 of thesubstrate processing apparatus 10 via the mass flow controller 103A andvia the valves 104A and 105A and further via the valve 106, while thenitrogen gas source 101B supplies a nitrogen gas to the gas ring 14 viathe mass flow controller 103N and via the valves 104N and 105N andfurther via the valve 106 coupled to the gas ring 14 commonly to the gassupply path of the Ar gas and the gas supply path of the nitrogen gas.Further, the oxygen gas source 101O supplies an oxygen gas to the gasring of the substrate processing apparatus 10 via the mass flowcontroller 103O and the valves 104O, 105O and the valve 106.

Further, the system 100 includes the microwave power source 112 thatsupplies the microwave power to the radial line slot antenna 15 via animpedance matcher 111.

Further, the heating mechanism 12A is provided in the stage 12 fortemperature control of the substrate W to be processed.

Further, the system 100 includes the evacuation system 11E coupled tothe evacuation port 11C via the adaptive pressure controller 11D.

Further, the system 100 includes the gate valve 11G cooperating with thesubstrate in/out opening 11 g provided on the processing vessel 11 forloading and unloading the substrate W to be processed to and from theprocessing vessel 11.

Further, it should be noted that there is provided a system controller100C that controls the mass flow controllers 103A, 103B, and 103O,valves 104A, 104N, 104O, 105A, 105N, 105O and 106, the heating mechanism12H, an evacuation pump not illustrated, and further the gate valve 11Gaccording to the program held therein, and the substrate processingapparatus 10 performs the foregoing nitridation processing or oxidationprocessing and nitridation processing of the oxide film under control ofthe controller 100C.

FIG. 8B shows the construction of the controller 100C.

Referring to FIG. 8B, the controller 100C is a general purpose computerand includes a CPU 1001, a memory 1002 holding a program and data, aninterface unit 1003 connected to the system 100, and an I/O interface1005 connected with each other by a system bus 1004, wherein thecomputer 100C is provided with the control program of the substrateprocessing system 100 from a recording medium 1006 such as an opticaldisk or a floppy disk or from a network 1007 and controls the substrateprocessing system 100 of FIG. 19A including the substrate processingapparatus 10 via the interface unit 1003.

Thus, the present invention also includes such a computer configured bythe program code means recorded on a processor-readable medium and alsothe processor readable medium that carries such a program code.

FIG. 9 shows a nitridation processing corresponding to FIG. 2C or FIG.7C conducted with the plasma substrate processing apparatus 10 of FIGS.1A and 1B under the control of the system controller 101C.

Referring to FIG. 8, the processing vessel 11 is evacuated in the step 1by controlling the evacuation system 11E and the adaptive pressurecontroller 11D, and the substrate W to be processed is introduced intothe processing vessel 11.

Next, in the step 2, the substrate W held on the stage 12 is heated to apredetermined temperature by energizing the heater 12 via the powersource 12C.

Next, in the step 3, the rare gas such as Ar is introduced into theprocessing vessel 11 from the gas source 101A by controlling the valves104A, 105A and 106 and the mass flow controller 103A, and the pressureinside the processing vessel 11 is controlled to a predeterminedpressure by controlling the adaptive pressure controller 11D.

Next, in the step 5, the microwave source 112 and the impedance matcher111 are controlled, and plasma is ignited in the processing vessel 11Ain correspondence to the processing space 11A.

Next, in the step 6, the nitrogen gas in the gas source 101N isintroduced into the processing vessel 11 by controlling the valves 104N,105N and 106 and further the mass flow controller 103N.

After the nitridation process, the plasma is deenergized in the step 7by controlling the microwave source 112 and the impedance matcher 111,and the supply of the plasma gas and the nitrogen gas is stopped bycontrolling the valves 104A, 104N, 105A, 105N, 106 and the mass flowcontrollers 103A and 1036B.

Further, in the step 9, the adaptive pressure controller 11D and theevacuation system 11E are controlled and the pressure inside theprocessing vessel 11 is controlled to a predetermined pressure fortaking out the substrate W thus processed.

Further, while the present invention has been described with regard topreferable embodiments, it should be noted that the present invention isnot limited to such specific embodiments but various variations andmodifications may be made without departing from the scope of theinvention described in the claims.

According to the present invention, it becomes possible to obtain anoxynitride film by a nitridation processing of an oxide film that usesnitrogen radicals excited by a microwave introduced by a planar antenna,such that the oxynitride film has optimum characteristics including theleakage current characteristics, by choosing the processing pressure inresponse to the initial thickness of the oxide film.

1-15. (canceled)
 16. A method for nitriding an oxide film, comprisingthe steps of: forming an oxide film on a substrate; forming plasma of amixed gas of a rare gas and a nitriding gas over said oxide film; andnitriding a surface of said oxide film by said plasma, said nitridingstep being conducted by said plasma formed under a pressure of 60 Pa ormore, said nitriding step thereby converting said oxide film into anoxynitride film.
 17. The method as claimed in claim 16, wherein saidstep of forming said oxide film is conducted by any of a thermalannealing process of said substrate or oxidation of said substrate byplasma containing oxygen.
 18. The method as claimed in claim 16, whereinsaid oxide film has a thickness of 1 nm or more.
 19. The method asclaimed in claim 16, wherein said step of nitriding said oxide film isconducted at a process temperature of 550° C. or less.
 20. A method fornitriding an oxide film, comprising the steps of: forming an oxide filmon a substrate; forming plasma of a mixed gas of a rare gas and anitriding gas on said oxide film; and nitriding a surface of said oxidefilm by said plasma, said nitriding step being conducted by said plasmaformed under a pressure of 60-130 Pa, said nitriding step therebyconverting said oxide film into an oxynitride film.
 21. The method asclaimed in claim 20, wherein said step of forming said oxide film isconducted by a thermal annealing process of said substrate or oxidationof said substrate by plasma containing oxygen.
 22. The method as claimedin claim 20, wherein said rare gas is any of a Kr gas or an Ar gas. 23.The method as claimed in claim 20, wherein said step of nitriding saidoxide film is conducted at a process temperature of 550° C. or less. 24.The method as claimed in claim 20, wherein said nitrogen concentrationis controlled such that no nitrogen is detected at said interface.
 25. Amethod for nitriding an oxide film, comprising the steps of: providing asubstrate carrying thereon an oxide film; forming plasma of a mixed gasof a rare gas and a nitriding gas on said oxide film; and nitriding asurface of said oxide film by said plasma, said nitriding step beingconducted by said plasma formed under a pressure of 60 Pa or less, saidnitriding step thereby converting said oxide film into an oxynitridefilm.
 26. The method as claimed in claim 25, wherein said oxide film isan oxide film formed by a thermal annealing process of said substrate oroxidation of said substrate by plasma containing oxygen.
 27. The methodas claimed in claim 25, wherein said oxide film has a thickness of 1 nmor more.
 28. The method as claimed in claim 25, wherein said nitridingstep is conducted with controlled nitrogen concentration such that thereis formed a peak of nitrogen concentration in said oxynitride film belowa top surface of said oxide film but above an interface of said oxidefilm and said substrate.
 29. A method for nitriding an oxide film,comprising the steps of: providing a substrate carrying thereon an oxidefilm; forming plasma of a mixed gas of a rare gas and a nitriding gas onsaid oxide film; and nitriding a surface of said oxide film by saidplasma, said nitriding step being conducted by said plasma formed undera pressure of 60-130 Pa, said nitriding step thereby converting saidoxide film into an oxynitride film.
 30. The method as claimed in claim29, wherein said oxide film is an oxide film formed by a thermalannealing process of said substrate or oxidation of said substrate byplasma containing oxygen.
 31. The method as claimed in claim 29, whereinsaid oxide film has a thickness of 1 nm or less.
 32. The method asclaimed in claim 29, wherein said step of nitriding said oxide film isconducted at a process temperature of 550° C. or less.